CA2080411A1

CA2080411A1 - Method of producing multilayer coatings, more particularly for lacquering of motor vehicules, having good adhesion between layers

Info

Publication number: CA2080411A1
Application number: CA002080411A
Authority: CA
Inventors: Bettina Vogt; Hans-Peter Patzschke; Werner Lenhard; Dietrich Saatweber
Original assignee: Individual
Current assignee: Axalta Coating Systems Germany GmbH and Co KG
Priority date: 1991-10-17
Filing date: 1992-10-13
Publication date: 1993-04-18
Also published as: ES2077324T3; JPH05208167A; KR930007520A; EP0537726B1; TW221453B; EP0537726A1; ATE124891T1; DE4134289A1; US5439710A; DE59202867D1

Abstract

Abstract A method of producing multilayer coatings, more particularly for lacquering of motor vehicl,es, in which at least three immediately adjacent layers with alternating effective change of the used binders are applied. The coating agents can be made polar e.g. by using resins containing ionic groups.

Description

~ 2~80~11 Herberts Gesellschaft mit beschrankter Haftung A method of producing multilayer coatings, more par~icularly for lacquering of motor vehicle~, ~ having good adhesion between layers The invention relates to manufacture of multilayer coatings, more particularly ~or lacquering of motor vehicles, having good adhesion between layers.

Multilayer coatings are universally known in the industry.
They are used for producing a lacquer structure which has various advantageous properties which cannot be obtained by using one coating agent only. In the car industry, for example, two component stopping media or electrodeposition coating stopping media are used ~n order to pro~ect t~e ~ ( p~,; h,ev / ~ ~~ c~v~S~
metal parts from corrosion L Fille ~ designed to compensate irregularities ~ the substrate and so obtain a smooth homogeneous surface ~ various kinds of substrate.
They are also designed to protect the stopping medium from gravel or other mechanical damage. The ~ coatings normally improve the appearance of ~he~substrate. They are single-layer or multi-layer coveringVlacquer coatingsO ~he multilayerYcoatings comprising a pigmented base layer covere~ with a clear lacquer layer.

Multilayer lacquer coatings of this kind are described e.g.
in EP-A-89 497. An aqueous anionic binder in a metallic base layer i5 applied to conventional substrates, followed by application of a normal conventional single-component (German abbreviation lK) or two-component (2K) clear lacquer.

To improve the efficiency of a complex multilayer lacquer structure, the individual layers are usually optimised with a view to their special intended application. To obtain a .... . . . . . .

2080~11 good overall result, however, the successive layers must be well adapted to one another. For example, the layers must adhere very firmly to one another~ More particularly, adhesion between the individual lacquer layers is required ~ to~e cl,;~,p;Ll,~ ~
under mechanical stress, e.g. from ~ her problem, which is also connec~ed with adhesion, is the resistance to ; S ~
"damp heat". It ~-~eYn-f~ that under various damp storage conditions, moisture may accumulate' ~ iht~r~
~ h ~ ~ V S'Y<S + e ~ S ,~
individual layers of la~q~cr~ ~lS results in loss of adhesion or blistering between the lacquer layers.
~d ~;o~ ~c~ s ne possibility of imp~oving the adhesion i l~v~ ;P~
in the coatin ~ ~he primers can optionally diffuse into the surface later, depending on the chemical structure, and thus increase the adhesion ~ the next layer of lacquer.
For example, DE-OS 39 32 744 describes the use of zircon-aluminate compositions to improve adhesion. It is also ~ 5iO h v~d ~t ~vs ~
known to use reactlve ~ e additives, however, have to be ~pecif1rc~l~i testedtfor each layerO ~ often ~ey have side-effects, e.g. tendency to form craters, which ~ /y prevent a good lacquer structure being obtained.

EP-A-O 421 247 describes a process in which two electrochemically deposited lacquer layers for improving the optical properties are described. An anionic layer (ATL) is first deposited, then stoved, provided with a second layer in the form of a cathodic electrodeposition lacquer coating Tl~ v~ v/~ 5 ~ orv~ v~r irf~
(KTL) and stoved. ~ u~ A~7r~ rre p~
t~e t~ l h~v~v errosion-~n~-tl~ appearance.i~ ~e~io~e~ i~ th~
no subsequent ~ layers are ~cscribc~
o~ tle p~,; ~e" I~ s~
o c~ s i~ J
In DE-OS 38 05 629 a ~ ~ the form of a coating agent based on an anionic binder is applied to a commercial KTL. The covering layer is a commercial alkyd/melamine covering layer. The aim of this lacquer structure is to improve the protection against gravel given by aqueous anti-gravel coating agents, by using special . . .

208~
resins. A conventional solvent-containing covering lacquer is used. The multiple coating has the usual weaknesses with regard to resistance to damp heat. A11 the anti-gravel layers in multilayer structures hitherto described consist of anionic binder systems.

The aim of the invention is to provide a method in which the structures of the binders in successive layers are well adapted to one another~^ a~ to obtain good adhesion between ~e layers and improved resistancelto *~mp ~ at~ e ~

This is achieved by the process constitut~ng the subject of the invention, in which at least three ~mc~ia~olil adjacent ,, ~ to~tQi~;l~ v~ S ~
( ~ h~ g~ ernating polarity are applied in order to produce multilayer coatings.

Preferably at least four ~tzrna ~ polar layers are applied, and particularly preferably the entire struct made up of ~lt~ nating polar~layers~ co~f~;~.'~ vc5;~
o~o~ e e~c~l~e cl~v~
Preferably the alternating structure is counted starting from the ~ layer of the multilayer structure.

"Aliernatin polarity" means that adjacent coatin agents or ;~e b~se~o~ ve5 i~ vi~ +l~;v e~c~ r c~1~v~le ;S o~;k -layers ~e ~ y, i.e. _~c-l~p -D~y~
T~e pol~it~- is the- 5U.~ ~L tl-~ pul~iLi~s uL-Lh~ ivldual t . ~6~6titU~ntDl ~I,e ~ 7 i~ t~e ~c~ ve ~o~ c l rh\~lS/ ~he rity of the layers is mainly determined by the content of polymers containing polar groups, e.g. ionic groups or groups convertible into ionic groups and optionally supported by groups having a strong dipole or a high dipole moment.
c~ ~v~
Preferably the resins comprising polar groups ~ke ~-~ a~l ~as~ a ~rt~f thc con~cnt of convcntio~al laequer rc3in~, e.g. binder resins, hardeners or cross-linking agents, paste 2~8~4~
resins, rheoloyy resins or other resin~ e components of polymers optionally contained in coating agents.

In the method according to the invention, it is preferable e.g. to use "anionic" and "cationic" coating ~ . The ~ q ~ e~ ~I s coating ~e~ of use according to the invention are preferably water- based. Hereinafter the invention will be described mainly with respect to the aforementioned preferred examples of coating ~ , but this is not a limitation.
~ao~ ;fS ~
TheVstability in~damp hea obtained by the process according to the invention is particularly surprising because the sU ~p ~s~ ve interfaces between the lacquer layers ar~eyiniti~ -in a -s~ v~s~ ev~/
salt-like ~ icularly sensitive to ~o;s~
~;~ls The anionic coating ~e~ for use according to the invention can e.g. be coating agents comprising lacquer bindersy anio~ic groups incorporated in the polymer skeleton ov covql~/y ~ff~
~-a rcact~ o~ ~ tive groups convertible into anionic groups. The cationlc coating agents can e.g. contain lacquer binders bearing cationic groups incorporated in the polymer skeleton by a reaction, or substituents convertible into cationic groups. According to the invention, not all the resins need contain ionic groups. It is sufficient if only a part of the resins contain ionic groups. Ionic additives or ionic pigments can assist the effect according to the invention. The anionic groups or groups convertible into anionic groups can e.g. be -COOH, -SO3H, -PO2R(OH) or -PO3H2. These groups can be converted into the corresponding anions by organic or inorganic bases. The cationic groups or groups convertible thereinto can e.g. be -NR3~, -NHR, -NH2 or -SR2~, where R~denotes e.g. C1 to C8-alkyl. The groups can be converted intovionic form by organic or inorganic acids or by alkylation. These ionic groups are preferably linked to the binder by covalent bonds.

,' ' ' ' " ' "~"""' ' ' '.

As already mentioned, use can also be made of components containing groups which are strong dipoles, e.g. have high dipole moments. Examples of such groups are: hydroxyl or ether or amide or urethane or urea or ester or nitrile or nitro groups or halogen atoms (e.g. chlorine and fluorine, as in the trifluoromethyl group).

The method according to the invention can e.g. be as follows. A coating agent containing e.g. cationic groups incorporated by a reaction is followed by a coating agent containing anionic groups and then by a cationic coating.
The reverse sequence is also possible; the important ~hT~ ~c~
is the alternating ~ e~o~ cG~e ~ J
b;~O~evs ~s~ .e-.f ~ y~v5~
~ov e~ /c, ~In-thc ~ ~ccording to the invention, ~ the first layer ~ a ueous corrosion-~cJi-~t~n~ ~t~ pY~C~ vO
Ia~ p~c~b/~ b,y ~/~o~t~ ~opo~'f7~. Fv t/,~ ~pP~4h~
-modium which is ~ Thi~ c~n ca~ry_ either anionic ~ (AT~) or c~tionic ~ (KTL) in thc e ~vc~ 4 . ~v ~h ~;v~f co~, ~y ~ye~-~ is q ~der. Another example,~fi~-ueous 2K-epoxyamlne ~cpplllg- p~ r wh ~ containSneutralised amino group-containing resins (cationic),tn ~he Tla~ UtablC CO~tilly dyt:llt.
~Y;~e~
A ~ is first applied, followed e.g. by an aqueous filler layer. An anionic stopping medium is covered by a cationic filler layer whereas a cationic stopping - medium is covered by an anionic filler layer.
~ . _ . .
The next layer can be an aqueous pigmented lacquer, e.g. an c~
aqueous metallic base U~e~ . In the case of the anionic co~t ~
filler layer the base ~ ationic, whereas in the case of the cationic filler layer the base ~ S
anionic.

The next layer can e.g. be a clear lacquer coating. This as before contains ~ppe~ ly-charg~ionic groups incorporated ~ ;c~ ve o p~os; ~/r ~h~v~ ~ f~ b~ o~ ~
in the binders ~y-a-~4R~ ~ n ~n-ic base lacquer is followed by a cationic clear~ q~r layer, whereas a eationic base ~eq~er is followed by an anionie elea~ ~Q~
er layer.

The following are examples ~f multilayer struetures aeeording to the invention:

A) B) eationie stopping medium anionie stopping medium anionie filler (p~;~e~/5~ v) eationic filler (pri~v~ ce~) eationie base la~e~ ~~ anionie base ~ac~ ~o~
anionie elear ]ao~r eo~ eationic clear ~ o~

~ .
C) D) aqueous eationic 2K
stopping~m,e~icu~m;p v~q~ cationie stopping medium anionie ~ ~lnter-mediate medium ~ anionie filler (pv~ V~e~ /s~
eationic co~crln glacqu~ eationic base ~3~ ~o~+
anionie powder clear lacquer Tl.e ~bo~Je 1ts~ v co~rOr;~t~5 a~e e~ $ o~ s~
s~ ce~ c~ y~v5 :~t,~ e ~o~s;~ ;~ovs ~V~Pa ;~c ~V~r~r.
_of_example ac~or~;ng ~ be altered by intermediate layers, e.g. additional anti-gravel intermediate layers or additional barrier layers 9~ other sequences of layers. According to the invention, at least three layers ~5~ ~
;~;C ~ o~5~
e applied. Prefer,ably the alternating structure is counted from the outermost~layer inwards~ v~c~ le pv;~ev l~yev .
ev b~se~
-~3Y~ coating~ag~ are preferred for environmental p~S~ to ~5e ,50/vv~-f b~s~ ~y~ ~s reasons, but ln~d~al r~atin~ ~g~nfc-~a~r of co~rse h~iY~ a `
~nv~nf;~al ~g~urc~ In this case ~13~, however, the v 1~90 v ~ v binders must have ~ ionic groups. "~q~ue~
COC!,~ V;~15 ~I,,;cL. ~ve -~a6~e~ systems" are coating ag~=irc~cnt i~ physically or colloidally dissolve ~or~-~r-~J~ L~r~ uL ~ iv~
te~ ~v ~1,~ v~ o~c ,'~

...

208~
~ater. The electric charge can be on the surfaces of colloidal or dispersed particles and can be produced by adding suitably charged emulsifiers. Binders containing ionic groups are preferred.

In aqueous systems some of the ionic groups are usually necessary for converting the binder into a water-dispersible form, whereas in the case of binders in organic solvents, the proportions of ionic groups can be smaller. Some of the ionic groups can optionally be ~eacted with cross-linking agents during chemical ~ ~c-l ~ ng ~he l~cqucr r 1~, or can be expelled in the form of cleavage products from the coating film. It is sufficient if some of the ionic or ionisable groups are still present after cross-linking or drying the applied lacquer film. All polar binder systems or combinations thereof described in the literature or familiar to the expert can be used to obtain an alternating layer structure.

Examples of usable binders and coatin agents will now be ~ 4~ ;c r~ O~O~ ~y~
listed. r~th~ ~site~-~Lu~ iy med,~ TL) are described e.g. in EP-A 12 463, DE-OS 27 28 470, EP-A 82 291, EP-A 234 395, US-A 48 08 658, DE-OS 27 28 470, DE-OS 36 15 810, EP-A
261 385, US-A 48 65 704, EP-A 193 685, EP-A 4090, EP-A-52 831, US-A 44 14 753, US-A 44 96 672 and EP-A 259 181. These are coating agents which contain binders comPrising~group~
Cq )~ C ~`f~.S ;~,~o//~ O~v.~ 5 ~- incorporated ~ ~ lnto cationic groups, e.g. -NH2, -NR~, -NR~+, -SR~ or-P~+. The resin bases thereof are e.g. acrylate resins, epoxy resins, polyethers or diene polyhydrocarbons such as butadiene oils, polyurethanes, polyamides or polyester resins. The binders are self~cross-linking or can react via admixed cross-linking agents. The cross-linking agents can e.g. be blocked isocyanates, melamine resins, phenolic resins, transesterification hardeners, unsaturated compounds or Michael hardeners, as described in the literature. The coating agents can also contain finely-ol ~ d ~ cross-linked or co-reacting, optionally melting 2080~1 powders with or without ionic groups.

Examples of aqueous coating agents for anodic electrodeposition coating (ATL) and corresponding binders comprising anionic groups are described in EP-A 21 014, DE-OS
28 24 418, US-A 41 72 822, US-A 42 20 568, DE-OS 27 37 174, EP-A 106 355, DE-A 27 37 174 or EP-A 21 014. The binder bases may e.g. be polyester resins, epoxy resin esters, polyurethane resins, polyacrylate resins or reaction products of maleic acid anhydride with unsaturated, natura~ or synthetic oils, e.g. butadiene oils. The binders can be self-cross-linking or co-reacting. The groups convertible into ionic groups can e.g. by carboxyl or phosphonium groups.
(' .
EP-A-319 841, for example, describes anti-corrosion stopping media in the form of aqueous 2K systems comprising a neutralised cationic urethane amine together with epoxy resins.

DE-OS 38 05 629 or US 49 68 536 describes examples of aqueous anti-gravel stopping media based on anionic binders.
Polyacrylates, polyesters and isocyanate systems are mentioned.

Examples of aqueous fillers containing anionic binders are described in EP-A 0 272 525, DE-OS 38 05 629, US-A 49 68 536, EP-A 427 028 and WO 89/00412. Polyacrylates, polyesters, epoxyamine adducts, maleic acid anhydride and fatty acid reaction products or polyurethane-containing binders are described. These are cross-linked with amino resins, phenolic -resins or isocyanate derivatives. Conventional pigments, fillers and lacquer additives are used.

Examples of cationic fillers are described in German patent application P 41 34 301.8 by the present applicants and having the same priority date. The fillers are coating agents containing conventional pigments, filling substances, lacquer .. . - . . . .................... . .

additives and water as the solvent, and contain binders on the bases of polyacrylates, polyurethanes, polyesters or polyurethane-urea resins together with cross-linking agents based on melamine resins or blocXed isocyanates. The binders contain amines and have a molecular weight between 500 and 200 000, an OH number of 10 to 400, an amine number of 20 to 200 and a Tg between -50 and 100. -~

The binders cross-link with the cross-linking agents via reactive NH or OH groups. Solubility in ~ater is obtained via the neutralisable amino groups. The glass transition temperature (Tg) of the binders influences the elasticity thereof. The finished coating agents are appli~d by conventional methods, ~ ~c~ ~e ~ e ~ o~

Water-based lacquers based on anionic binders are described e.g. in EP-A 38 127, US-A 44 03 003, US-A 45 39 363, EP-A 71 070, EP-A 195 931, US-A 47 30 020, EP-A 238 108, EP-A-21 414, EP-A 89 497, US-A 44 89 135, US-A 45 58 090, EP-A 228 003, EP-A 256 540 and EP-A 260 444. The binders can be ionic microgels or co-reacting ionic polymers. The coating agents can dry under physical conditions or can optionally contain cross-linking agents or can be self-cross-linking. The binder bases are e.g. polymers of unsaturated monomers such as (meth)acrylic acid derivatives, polyesters, polyethers, polyurethanes or epoxy resin reaction products, as described.
t.
Examples of cationic water-based lacquers are descri~ed in DE
patent applieation 40 11 633. The substances are binders based on polyurethanes, polyesters, polyurethane-urea resins or polymers of unsaturated monomers such as (meth)acrylic aeid derivatives eontaining amino groups instead of free carboxyl groups. Base lacquers can be formulated from these binders by adding neutralising agents or pigments, fillers, catalysts and/or additives. The binders ean optionally be cross-linked via known amine formaldehyde resins or bloeked isocyanates.
These base laequers can be applied by conventional techniques.

~8~
Binders for water-based lacquers, if they have good resistance to weathering, can also be converted into covering lacquer coatings. However, it is necessary to choose binder systems which can be cross-linked with one another by a chemical reaction. No additional clear lacc~uer coating need be applied~ ~ ~v ~h;~ ~ ~V~O~ e ~

Examples of water-dilutable clear lacquers containing anionic groups are described in DE-OS 39 10 829, US-A 50 15 688, DE-OS
25 57 434, US-A 39 53 643, DE-OS 37 12 442 or DE-OS 40 27 594.
The substances are preferably carboxyl group-containing polymers based on polyesters, polyacrylates or polyurethanes and reacting with known cross-linking agents, optionally after heating, to form the clear lacquer coatings.

Examples of cationic clear lacquers are described in German patent application P 41 34 290.9 by the same applicants and having the same priority date. They are formulated on the basis of polymers of unsaturated monomers, e.g. acrylate resins. The binders must contain basic groups for converting into cationic groups. The properties of the lacquer can be adjusted via the molecular weight, glass transition temperature and the viscosity of the binders. The binders . ~ v ~ ~ .. vc ~
become cross-linked~ ~ groups );~p~ratc~ b~t ,~lr~, e.g. OH groups, using blocked isocyanates or melamine resins as the cross-linking agents.

Examples of powder clear lacquer binders containing ionic groups are mentioned in US-A 3 787 521, US-A 4 091 048, DE-OS
24 41 753 or DE-OS 25 09 410. The substances are e.g.
acrylate resins containing epoxy groups in the side chain.
These react, when melted, e.g. with polycarboxyl group-containing polymers or anhydride group-containing substances to form ester structures. Alternatively other cross-linking yroups can be used, e.g. primary OH groups. Even after cross-linking, the films still contain polar groups such as COOH or OH groups.

208~
The binders and coating agents listed hereinbefore by way o~
example can contain conventional pigments, catalysts or other ed for obtaining optical or technological effects or influence the properties during application. The effect according to the invention is not substantially influenced, or may even be intensified, by the additional constituents.

In one preferred embodiment, carboxyl group-containing powder lacquers are used as the clear lacquer coating. It is also preferred to use cationic water-clear lacquers. It is also preferred to use cationic water-based lacquers in the multilayer lacquer coating.
!

Some particularly preferred embodiments are multilayer structures contain~n~ a~l ~ eous anionic clear ~ based on acrylic/melamine resin or acrylic/isocyanate, ~ ~ ng cationic water-based lacquer based on aminopolyur(ethanes or aminoacrylate resins including an aqueous anion on Polyesters or epoxidised/urethanised alkyd resins. Another ~ ~ov ~ f ~ o~ vc ~ ~ ;*I,e~ OL~ ~ o..~,~f~
example~of a struct~r~ ~snta~n~fa ~3~3r-~-c water--clear lacquer based on aminoacrylate resin or aminopol~yurethan , ~ .A. ,"~
b~s~ coqt l~yc v o." ~ b~
an anionic water-based ~ olyester resins and/or ~ lyurethane resins, ~ an aqueous cationic fille ~ sed on amino epoxy resin.
~p~;~ev~v~yc~v) The coatings manufactured according to the invention are applied in known manner, e.g. by painting, dipping, electrodeposition coating or spraying. To ~ n~, the coating agents are adjusted to a suitable viscosity and a suitable solid content, ~ The individual lacquer C~rvg~ O~ O~ /~ O~
layers are cross-linked~ ~ prlor ar~ l.e: optionally at elevated temperature or at room temperature, or the lacque`r layers are applied wet-in-wet and stoved together. The coating agents can either dry under physical conditions and/or can be chemically cross-linked. They can be pigmented or non-pigmented when used. They can be formulated on the basis of 2~8~
one-component or two-component systems.

The layer thicknesses are preferably < 40 ~m for the stopping medium, < 130 ~m for the filler, < 25 ~m for the base lacquer and < 100 ~m for the clear lacquer. Other additional coating layers, e.g. anti-gravel coating agents or adhesive stopping media, can be applied for their respective purposes.
I~y~ h~ o~ c~ . e ~ t~
The ho~,~ost ~F^ lal~ar of thc - m~ltLlayer ld~U~L ~Udt~ must be adapted to the properties of the substrate, e.g. by adding ve~ t`~
~ requently necessary in plastics lacquers) or via thei.r composition. For example, binders containing anionic groups are par-ticularly suitable for electrophoretic aluminium coating. The multilayer coatings according to the invention, irrespective of their other properties, have good adhesion between layers. This is particularly noticeable in gravel tests or adhesion tests (e.g. criss-cross cut to DIN 53151) and in stability tests under constant air conditions (e.g. DIN
50017).
Sy~ e~_ b ~ s ~ ~
The coating ~ are preferably ~ormul~t^d ~n an ~
Alternatively, individual lacquer layers can contain solvents and be formulated with a high solid content or can be solvent-free systems. In this case also, however, care must be taken that at least parts of the resins, e.g. the binders, carry polar, optionally ionic, groups incorporated by a reaction. Optionally, two-component coating agents can also be used.

The aforementioned multilayer lacquers are particularly suitable ~or use on cars or in the car ancillary industries.
Other articles can be coated correspondingly. The substrate~
can be all those conventionally used in the car industry, e.g.
metal substrates such as steel or aluminium or plastics substrates, e.g. polyurethane, polyamide, polycarbonate or polyolefins. The resulting multilayer coatings are gravel-resistant and have a good appearance.

. 15 .. . . .
, Examples 2 0 ~

In the multilayer structures described hereinafter, the individual coating agents used were as follows:
Co~vc,~I/y ~ /e A) ~ ~_ ~ o~=:ng ~Ats for cataphoretic electrodeposition coating based on aminoepoxy resin and blocked isocyanate hardeners as described in DE-A-27 01 002.

B) Anionic hydrofillers (DE-OS 38 05 629, Example 1): aqueous lacquer based on an amine-neutralised polyester using blocked polyisocyanate as a hardener.

C) Anionic water-based lacquer (EP-A-89 497, Example 6):
aqueous coating agent based on anionic polyurethane dispersions in combination with acrylated polyesters.

D) Cationic water-based lacquer (DE-OS 40 11 623, Example 1):
aqueous coating agent based on amino acrylates as described hereinafter.

E) Anionic water-clear lacquer (DE-OS 39 10 829, Example 3):
aqueous covering lacquer based on hydroxy-functional acrylate comprising cross-linking agents in the form of neutralised carboxylic acid groups and melamine resin.

F) Anionic conventional lK clear lacquer (commercial product): conventional clear lacquer based on carboxy-functional and hydroxy-functional acrylate with melamine resin cross-linking agent.

ExamPle of manufacture 1 ~mino-polYfmethlacrvlate resin) 725 g of butoxyethanol were heated to 110C under inert gas, using a reflux condenser~

,, .. , ..... . . , , . , -- . . .

A mixture of 192 g hydroxyethyl acrylate, ~37 g butanedl Q
monoacrylate, 228 g glycidyl methacrylate, 364 g 2-ethyl hexyl acrylate 439 g butyl methacrylate, 438 g methyl methacrylate, 90 g styrene and 44 g azo-bis-isobutyronitrile were added within 3 hours. The mixture was then left at 110C for 1 hour, 6 g of azo-bis-isobutyronitrile was added and the process was repeated after another hour. After 3 hours at 110C, the measured content of solids was 72.2 wt.% and after dilution to 60 wt.% with butoxyethanol the measured viscosity was 2.14 Pa.s at 25C. After cooling to 50C, a mixture of 120 g diethylamine and 201 g isopropanol was quickly added (1.10 mol amine to 1.00 mol epoxide). After 30 minutes the mixture was heated to 65C, kept at that temperature for 2 hours, then heated to 105 to 110C and kept at that temperature for 3 hours. A~ter cooling to 80C, the isopropanol and excess amine were carefully distilled off in vacuo. The content of solids was adjusted to about 78 wt.%
with butoxyethanol.
~ ~ ~ J ~A ~.e ,,,,Jr o~ I G L~ V~ V~I G ~ev, s ~
Fin~-~aluc-s-;-: 78.7 wt.% (30 minutes' heating to 150C) v ~Amine ~ e~: 45 mg KOH per g solid resin Viscosity: 3.44 Pa.s. (60 wt.% in butoxyethanol at 25C).

Example D (cationic water-base lacquer) 555 g of titanium dioxide were added to 945 g of amino-poly (meth)acrylate resin as per Example of manufacture 1 and dispersed in the dissolver for 5 minutes. The paste was then ground in a pearl mill at temperatures up to 60C for 40 minutes.

Solids: 86.6 wt.% (after 30 minutes' heating to 150C) ,. , , . ~ - - . , . , - ....... , : , ,, . . ~ . . .

2 ~
Pigment-binder ratio = 0.75 : 1.

77z g of the paste was thoroughly agitated in the dissolver together with 111 g higher-molecular melamine resin (80%
dissol~ed in isobutanol) containing higher-molecular methoxy-imino groups and a catalyst in the form of 17.7 g of an amine-blocked sulphonic acid (25%). The mixture was then further diluted in the dissolver with vigorous agitation, first with 7.6 g of formic acid (85~) and then slowly with 142 g of completely demineralised water. After standing overnight, 100 g of the lacquer was adjusted to a spray viscosity of 30 seconds with 62 g completely demineralised water in a flow cup (DIN 53211).

Exam~le of manufacture 2 (PolYester oliqomers~

336.7 g trimethylol propane, 366.8 g adipic acid and 297 g hexanediol were esterified to an acid number of 20 in the melt at 180C to 230C in a 2-litre three-necked flask provided with an agitator, separator, thermometer and reflux condenser.
The mixture was then condensed in vacuo to an acid number < 1.5. The resulting product had a stoviny residue of 94.5%
(1 hour, 150C), a viscosity of 3200 mPas (100%), a hydroxyl number of 460 and a colour index of 30 Hazen.

Exam~le of manufacture 3 (polyester oliqomer polyacrYlates) 717 g of polyester oligomer from Example 2 was reflux-heated to 81C with 597 g ethanol in a 4-litre three-necked flask equipped with an agitator, reflux condenser, dropping funnel and thermometer. Next, a mixture of 552 g butanediol monoacrylate, 996 g tert. butyl acrylate, 74 g acrylic acid and 50 g of 2,2-azo-bis-2-methyl butyronitrile was added dropwise in 4 hours and additionally polymerised for a further 4 hours.

.. .. ...

2 ~
~he product had a stoving residue of 79.8% (1 h, 150C) at a viscosit~ of 7200 mPas (DIN 53015), an acid number of 26.3, an OH number of 231 and a colo~r index of 60 Hazen.

Exam~le of manufacture 4 717 g of the oligomer in Example 1 and 311 g butoxyethanol were placed in a 4-litre three-necked flask equipped with agitator, reflux condenser, dropping funnel and thermometer and heated to 140~. Next, a mixture of 552 g butanediol monoacrylate, 946 g tert.-butyl acrylate, 74 g acrylic acid and 100 g Trigonox C (tert.-butyl perbenzoate) was added dropwise in 4 hours and polymerised for an additional 4 hours.

The product had a stoving residue of 84.0% (1 hour, 150C) as per DIN 53182, a viscosity of 15830 mPas (DIN 53015), an acid number of 38.0 (DIN 53402), an OH number of 231 (DIN 53240) and a colour coefficient of 60 Hazen (DIN 53409).

ExamPle E 1 (anionic water-clear lacquer) 651 g of the polyester oligomer polyacrylate 1 described in Example 3, 348 g of a high imino-functional melamine resin and 152.8 g ethanol were thoroughly pre-mixed in a laboratory agitator and a mixture of 50.7 g butoxyethanol, 20-? g of a benzotriazole-type W absorber and 13.7 g of a HALS-type radical-trapping agent were added with further agitation. The mixture was then agitated and neutralised with 27 g dimethyl ethanolamine, agitated for a further 15 minutes and then diluted with a mixture of 973 g completely demineralised water and 15.4 g ethanol. The lacquer had a viscosity of 31 seconds (measured in a DIN-4 beaker at 20C) and a pH of 9Ø

ExamPle E 2 639.7 g of the resin solution described in Example 4 was .

.. . ... . .. .

2~8~
homogeneously mixed in a hi~h-speed ayitator with 375.3 g of a commercial wat~r-dilutable melamine resin containing methoxymethyl imino groups and 90.5 g butoxyethanol. Next, 37.6 g dimethyl ethanolamine was added to the resin and solvent mixture and agitated for 15 minutes. A further 37.27 g of a mixture of 59.9 wt.% of a benzotriazole-type W
absorber and 40.1 wt.% of a HALS-type radical-trapping agent were added and the mixture was agitated until clear and free from streaks. Next, 534.1 g of completely demineralised water was added with agitation within 5 minutes. After 24 hours the lacquer had a viscosity of 50 seconds (DIN 4 beaker at 20C) and a pH of 8.6. The lacquer was stable in storage for more than 3 months.

In order to apply the individual lacquer layers to the substrate, the lacquer was ad~usted with completely demineralised water or solvent to the viscosity for processing and applied by the usual techniques.

The stopping medium was applied electrophoretically and the remaining layers were applied by a spray robot. Alternatively they can be applied by means of other equipment such as flow-beaker pistols, a pressure vessel or high-rotation bells. The layers were then stoved as described in Table 1. The KTL and fillers were stoved individually after application, whereas the base layer and the clear lacquer layer were applied wet-in-wet as follows:

The base lacquer was pre-dried at 80C for 6 minutes and then covered with about 40 ~m of water-clear lacquer. The lacquer was pre-gelled at 80C for 15 minutes, after which the two layers were stoved together at 120C for 20 minutes.

2080~
Table 1:

~TL ~iller Base Clear lacquer lacquer _______________________________________________________________________ __ Stoving te~perature 30' 180C 20' 160C 6' 80C 20' 120C
1) .
Layer thi~kne~ 2) 20 ~ 1 35 + 1 15 + 1 40 ~ 1 1) In mLnutes and C
2) In ~m The previously-described coating agents A to F were used to produce various multilayer structures. The structures are listed in Table 2. Examples 3 and 4 are according to the invention.

The following technological test results for adhesion are given: the criss-cross cut (2 mm) to DIN 53151 and the mechanical stress test using the VDA gravel-testing apparatus (1 bar, 1000 g) to DIN 53230. The evaluation scale is from 1 to 6, 1 denoting a very good and 6 denoting a very poor adhesive connection. The products were stored to DIN 50017 under constant air conditions (240 h, 40C) in order to describe the damp-heat box stress, i.e. to evaluate the swelling and possibility of regeneration.

:. . . . .

.

2 n ~
Table 2:

Structures No~ 1 No. 2 No. 3 No. 4 __________~_____________.____________________________ ___________________ 5topping medium A A A A
_________________________________________________________________________ Flller B B B B
_________________________________________________________________________ Base lacquer C C D D
_________________________________________________________________________ Clear lacquer F E F E
___________________________ _____________________________________________ TEST DATA
Criga-crogg cut 2 mm ~DIN 53151) 2 2 1-2 0-1 __________________________________.____________________ Gravel l bar, 1000 g ,_________________________________________________________________________ h~ f ;D~ 5~
Dam~het~ bo7~ -1. Swelling Large blisters Considerable Small No > 80 ~m swelling, blisters blisters, Considerable change in ~ 40 ~m slight swelling ~hade of Slight surface colour surface ~welling ~welling _______________________________________________________ 2. Regeneration in: 24 h useless 3 - 4 h 1 - 2 h > 24 h ____________________________________________________ ___________________ .,.. . . . . -

Claims

1. A method of manufacturing multilayer coatings by applying a number of coating layers based on organic resins in succession to a substrate for coating, characterised in that at least three immediately adjacent layers are applied, at least some of the resins in these three layers having polar groups, the polarity of the polar groups of the resins within each layer being the same and the resins in immediately adjacent layers containing polar groups of opposite polarity, resulting in a layer structure having alternating polarity of the resins.

2. A method according to claim 1, characterised in that at least four immediately adjacent layers with alternating polarity are applied.

3. A method according to claim 1 or 2, characterised in that the layers with alternating polarity are counted outwards from the surface of the finished multilayer coating.

4. A method according to any of the preceding claims, characterised in that all the layers in the multilayer coating have alternating polarity.

5. A method according to any of the preceding claims, characterised in that the polar groups are ionic groups or groups convertible into ionic groups and/or groups with a strong dipole.

6. A method according to any of the preceding claims, characterised in that the resins are binder resins, hardener resins, paste resins and/or rheology resins.

7. A method according to any of the preceding claims, characterised in that at least one layer based on an water based coating agent is used in the alternating structure.

8. A method according to claim 7, characterised in that water based coating agents are used in at least two layers of the alternating structure.

9. A method according to any of the preceding claims, characterised in that only water based coating agents are used in the alternating structure.

10. A method according to any of the preceding claims, characterised in that water based coating agents are used in all layers.

11. A method according to claims 7 to 10, characterised in that the water based coating agents contain resins having ionic groups.

12. A method according to any of the preceding claims, characterised in that the adjacent layers having alternating polarity comprise a base lacquer layer covered by a clear lacquer layer, the base lacquer layer optionally being formed on a filler layer.

13. A method according to claim 11 or 12, characterised in that the clear lacquer is a powder lacquer.

14. A method according to claim 11, 12 or 13, characterised in that the clear lacquer contains a resin comprising cationic groups.

15. A method according to any of claims 11 to 14, characterised in that the base lacquer contains a resin comprising cationic groups.

16. A method according to any of claims 11 to 15, characterised by use of a filler containing a resin comprising cationic groups.

17. A method according to any of the preceding claims, characterised in that it is used for lacquering motor vehicles.

18. A multilayer coating produced by the method according to any of claims 1 to 17.